In the power bridge circuit device or the like, a driving circuit is provided with respect to each of a plurality of semiconductor devices that receive switching commands from an overall control system, for driving a gate or base of the semiconductor device in response to the switching commands. Further, an abnormality detection circuit and protection circuit for protecting the semiconductor device from various types of abnormalities and troubles that may occur during the operation of the device is conveniently incorporated, along with the above driving circuit, into an integrated circuit for the semiconductor device, to thus provide one chip. The abnormality detection circuit is adapted to detect overcurrent flowing through the semiconductor device, or an excessive increase in the temperature of the device or chip. When an abnormality is detected by this circuit, the protection circuit usually stops or turns off the switching operation of the semiconductor device, to automatically shut off current flowing through the device immediately after the detection of the abnormality or a certain time after the detection.
In addition to these abnormality detection circuit and protection circuit, another circuit is conventionally incorporated which serves to notify the overall control system that an abnormality has been detected, and that a command to stop the operation of the semiconductor device has been generated based on the detection. In response to this notification, the overall control system is able to stop or interrupt, as needed, the switching commands that have been given to the semiconductor device. This ensures that the semiconductor device never performs its switching operation and can be thus surely protected, even in the worst situations in which the semiconductor device does not receive a command to stop its operation despite the fact that an abnormality has been detected, or a circuit for stopping the operation of the device does not normally operate even if it receives such a command.
Although the conventional abnormality detection and protection circuit is able to stop the switching operation of the semiconductor device for its protection with considerably high reliability upon occurrence of abnormalities, it has been required in recent years to provide more rational protection in view of the operation of the whole circuit device into which a plurality of semiconductor devices are incorporated, rather than merely providing protection for each of the semiconductor devices. In the case where a power inverter device for driving a motor consists of a bridge circuit in which semiconductor devices are incorporated in respective arms thereof, for example, the inverter device will not normally perform its function if the operation of the individual semiconductor device in each of the arms is suddenly stopped in no conjunction with the other arms, except when the abnormality is of a type that requires emergency stop. Depending upon the type of a machine coupled to the motor, it is not permitted to suddenly stop the operations of the semiconductor devices in all of the arms of the inverter at the same time and eliminate the driving force for the motor.